Time delay circuit



Jan. 15, 1946. F. E. BARTHOLY 2,393,014

TIME DELAY CIRCUIT Filed March 20, 1943 WITNESSES: INVENTOR 44 p. 7M 4 WWe,

ATTORNE Patented Jan. 15, 1946 UNITED STATES PATENT OFFICE rnvm DELAYcmcurr Frederick E. Bartholy, Wilkinsburg, Pa., assignor to-Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporationof Pennsylvania This invention relates to electrical relay circuits andmore particularly to a time delay circuit operating in connectiontherewith.

In electrical and industrial operations sensitive relay devices arefrequently employed for indicating the occurrence of certain phenomena.For example, capacity operated relays or photoelectric devices are usedto indicate the presence on the passing of diflerent objects, by thecontrol of lights or by soundingan alarm. It is often desirable that theeffect produced by the energization of the sensitive relay or thephotocell be prolonged, particularly if the energlzation is of a veryshort duration. I

In the control of lights for display purposes or in the sounding ofalarms used in protective installations the control effect may only bemomentary such as the passing of a person in front of a show window,etc. If lights are to be lit or an alarm is to be sounded, it isnecessary to provide means whereby the above eflects are produced notonly during the energization of the relay system while the presence ofthe person within a narrow confine is observed but also that after thecause is removed the effect shall persist for a predetermined time andthereafter the system shall again be responsive to repeatedenersizations.

This application is a continuation-in-part of application, Serial No.388,105 and is directed to a particular feature of the invention whichpermits a cumulative time delay action upon momentary impulses which mayarrive in succession following the first actuating impulse and duringthe delay time preset for the ensuing operation.

A particular feature of this invention is that in delay systems of thetype mentioned the desired eifect caused by energization of shortduration may be extended for a predetermined time and thereafter thesystem is restored automatically to a receptive condition for asuccessive enerization.

Another feature of thisinvention is that while the desired eifect isproduced within the predetermined delay period energization of thesystem during such time will automatically extend the time intervaluntil no energization appears within the delay period whereupon thesystem isagain automatically restored to receptive condition.

An advantage of the system in accordance with this invention is that thesystem may also be restored at any time during operation to a receptivecondition without interfering with the predetermined time for the emu-m8operation.

.eflect of momentary closures.

The invention contemplates a circuit arrangement for a time delay devicein connection with a primary actuating element whereby the actuationthereof closes the circuit and simultaneously initiates the operation ofthe time delay element.

The circuit is automatically held closed until the time delay deviceceases to function whereupon the circuit is automatically opened and thetime delay device restored. Meansare provided for restoring the systemat will at any time during the function of the time delay device to itsstarting condition without interfering with the predetermined timeintervals of successive operations.

The invention also provides for cumulative excitation of the time delayelement if the primary actuating means is momentarily closed or as longas it is closed, whereby the delay time is only eflective when theprimary actuating means remains open over the entire delay period.

Other features and advantages will be apparent from the followingdescription of the invention, pointed out in particularity by theappended claims, and taken in connection with the accompanying drawingin which the single figure diagrammatically illustrates an embodiment ofthe invention applied to an electrical circuit closim: element.

The electrical circuit closing element in the application above referredto was represented by a capacity operated relay in order to show a dovice which may operate only momentarily. The object of the invention inthe former case as well as in this instance is to register an extendedFor the sake of simplified illustration, the circuit closing element isshown here merely as a manually operable switch. It is to be understoodthat this switch may represent various types of circuit closing devicesand forms no part of the present inventionnor is it considered alimitation regarding the application of the time delay circuit about tobe described.

In its broad aspect, the invention provides an impulse actuated devicewhich upon energization by a first impulse will perform a certainoperation for a certain allotted time. The time is preset and everysuccessive impulse arriving within the preset time will extend the timeto begin anew until no other impulse is received after the last impulse,during the time preset for operation. The device is automatically resetafter the time element has completed its full or cumulative actuationperiod.

Operation in the manner above stated is often ample, in automatic gateopening controlled by photocells, timing detilized to keep the gate openfor a defiafter energization of the cell in order ow for the person toreach and pass through te. During this predetermined time interer'orethe closure of the gate another person the first one may cause aphotocell and the time delay for closure must be ended until the lastnamed person will pass through the gate. In such cases, cumulative timedelay is necessary since the actuating impulses cannot be so distributedas to appear after each closure of the gate.

ring to the drawing the switch repre- "he impulse device which whenclosed coms a circuit between power supply conductors it to the winding2| of the electromagnetlc switch 2E, The latter has a plurality ofcontacts among which 28 and 28 are in parallel with contacts 3 and 3 andlock the circuit so that the winding 2i remains energized after theswitch I is released from engagement with contacts 3 and 2. Contacts 29and 29 of the switch 20 complete the circuit to the load elements shownh re by of example as lamps I8.

is desired that upon momentary actuation of the switch l, the lamps l8shall remain energized for a definite period of time, and that afterthis time elapses and no other closure of the switch i occurs, the loadshall be disconnected and the circuit returned to its original receptivecondition. Moreover, it is desired that should the switch i be energizedagain during the time interval of operation, the time preset for theenergization of the lamps l8 shall be extended again to the sourcepredetermined time starting from the last actuation period. In otherwords, each actuation of the switch causing only momentary bridgin ofcontacts 3 and 3' and D and 50' shall renew the time period irrespectiveof the time elapsed since the energization of the lamps l8. This featureshall be further described in connection with the operation of the timedelay circuit. The contacts 3B and 30 of the switch 20 when the winding2% is not energized maintain the grid of an electron discharge device 32connected to the conductor l4. The discharge deinay be of the typeincluding a rectifier porcomprising an anode 33 and cathode 34 and trodeportion comprising the cathode 35, con.-

EL bu trol rid screen grid 36 and the anode 31. his type of tube, due toits compactness, is suitc for the application here intended, althoughtubes may as well be used, and it is not c rectifier portion is utilizedto provide di current potential for the elements of the tetrcde portionand is connected between conductors i4 and M in series with a loadresistor hich is shunted by a filter condenser 39 of St. hole size. Thefilament 3 may also be energized directly from the lines M and I4through a suitable series resistor IS. The cathode 35 is connected to apoint on the load resistor 38 by slider anode 3? is connected in serieswith the Winding All of the relay 25 to the cathode 34, which is thehighest positive potential or the rectified voltage output. The screengrid 36 is also connected to this point. The potential for e anodesupply will he in effect the portion of sister designated by the letterA between 3-! and the slider 35' whereas the portion between theconductor I4 and the slider 35' designated by the letter B will be of I.potential more negative than the cathode 35. Consequently, theconnection through the contacts 30 and 30 of the magnetic switch 20 orthrough the contacts 50 and 50' of the switch I will place the grid 3|at a potential which is negative with respect to the cathode 35. Thegrid 3| is also connected through a resistance capacity networkcomprising the resistor 4| shunted by the condenser 42 to the cathode35.

Describing the operation of the time delay circuit, let it be assumedthat the contacts 3 and 3' of the switch l are open and the switch 20 isin the open position as shown in the figure. Only contacts 30 and 30 areclosed whereby the grid 3| is connected to the negative terminal 0! theanode supply source, thatis, the resistor ll. The voltage drop acrossportion B of the resistor 38 is so chosen that the grid is biasedsufliclently negative to reduce the anode current either to zero or tosuch a small value which will not energize the winding 40 of the relay25. The con tacts 24 and 24 of the latter are, normally, closedsimilarly as the contacts 22 and 22 of the push button switch 23. Theload circuit to be controlled comprising the lamps I8 is deenerglzedfrom the line H and I4 due to the open contacts 29 and 29' of the switch20. The entire system is at rest.

A momentary closure of the switch bridging the contacts 3 and 3' willenergize the winding 2| and contacts 28 and 28' close the circuitpermanently to the winding 2| so that further opening of the contacts 3and 3' have no eilect as far as the switch 20 is concerned, which now islocked in position, being energized directly from the line.Simultaneously the contacts 29 and 23 are also closed and the lamps I8are now supplied with current from the conductors ll andll. The closureof contacts 28 and 28' and 29 and 29, is accompanied by the opening ofcontacts 30 and 30', whereby the grid 3| is disconnected from thenegative side of the supply source. The grid circuit has now a returnpath solely to the cathode 35 through the resistor I. The latter incombination with the condenser 42 provides the necessary time constantsince the charge accumulated by the condenser 42 when the contacts 30and 30 were closed must first discharge through the resistor 4|, anduntil such time as the discharge takes place'there is a progressivedecreasing negative bias on the grid 3|. The

- time of discharge of the condenser can be regulated by the slider 45of the resistor ll which will vary the effective resistance throughwhich the capacity 42 must discharge. As the condenser discharges thenegative bias on the grid 3| will be progressively diminshed and anodecurrent oi the tube 32 will correspondingly rise until a value isreached which is sufilclent to actuate the winding 40 of the relay 25 toopen the contacts 2Land 24. When these contacts are opened, the winding2| of the switch 20 is deenergized being disconnected from the conductorH and the switch 20 will resume the position shown in the drawing,closing the contacts 30 and 30' and opening the others. Closure oi thesecontacts instantaneously puts a negative bias on the grid 3|, Theopening or the other contacts disconnects the short circuit of thecontacts 3 and 3' and removes the load circuit from the lines I4 and H.

The switch I also actuates contacts III and 30' which are essentially inparallel with contacts ll and 80' or the switch 20. Consequently closureof the iormer contacts will connect the'grid- II to the conducto llthereby placing the negative side of the voltage dividersection B on thegrid electrode II which will instantly charge the condenser IL Thepurpose 0! this operation oi the switch I is to produce the desiredcumulative eiiect and cause resetting of the time element every time theswitch I is actuated. When the contacts 3| and III are open and thecondenser 42 begins to discharge through the resistance ll, the timeconstant oi the circuit determined by these elements will be reset everytime the switch I is de- Consequently, whenever the contacts I! and BIare momentarily closed, the preset time element determined by thecondenser 42 and resistor It shall begin anew and will hold theenergization oi the load it until ior the time preset no actuation ofthe switch I occurs. As described before. when the condenser 42discharses through the resistor ll, the grid ll is eiiectively atcathode potential which permits the desired anode current conductivityto actuate the reset relay II disconnecting the load ll irom theenergizing circuit and also causing complete resetting of the 5 systemfor the next ensuing impulse by the swikhl.

The entire system may also be reset any time if desired by openingmomentarily the switch 23.

In a practical embodiment of the. invention, the following circuitconstants were utilizedr Resistor l l-5 megohms Portion 3-5.000 ohmsCondenser 42-42 microiarads Condenser 38-16 microiarads.

The tube used was an RCA type 12A7, diodevpentode. A maximum delay ofapproximately one hour'was obtained between the time of operation 01 therelay I to the resetting of the system.

I claim as my invention: 1. In an electrical control system, a circuitclosing element operable ior momentary action. a circuit energizedthereby including a current ment, means tor extending thev actuationtime of said circuit after momentary actuation-oi said circuit closingelement comprising contact actuated by said switch for connecting saidenergizing coil to said source, normally closed contacts in seriesbetween said source and said energizing coil, delay action means havinga predetermined time interval of operatiommeans actuated by said switchfor initiating the start of operation time of said delay action meansupon closure oi said switch and means actuated by said vdelay actionmeans for opening said contacts and thereby deenergizing said circuitafter said lapse of time, said initiating means being operable tocondition said delay action means for recurrent operation and contactmeans operable in conjunction with the actuation of said circuit closinelement for restoring the start oi operation time 01 said delay actionmeans whereby the delay action of said delay action means is cumulativefor repeated momentary actuations.

2. In an electrical control system, a circuit clos ing element operablefor momentary action, a circuit energized thereby including a currentsource, a switch, an energizing coil for said element, means forextending the actuation time of said circuit aiter momentary actuation0! said circuit closing element comprising contact means actuated bysaid switch ior connecting said energizing coil to said source, normallyclosed contacts in series between said source and said energizing coil,delay action means comprising a vacuum tube having anode, cathode andgrid electrodes, a source of operating potentials therefor including avoltage for biasing said grid electrode negative with respect to saidcathode whereby space current flow through said tube is substantiallyprevented, a circuit of predetermined time constant connected betweensaid grid and said cathode, means for disconnecting said grid from saidbias source upon closure of said switch thereby eflectively placing saidtime constant circuit in 'operation and means operable upon spacecurrent flow in said tube for opening said contacts thereby deenergizing said first-mentioned circuit, and means to;- connecting saidgrid to said bias source upon opening or said circuit closing. elementfor restorcs ing the start-oi operation time of said delay acsourcc, aswitch, an energizing coil tor said ele- I FREDERICK E. BARTHOLY.

